Abstract—Billions of people have inhaled numerous harmful gases while driving or sitting both inside and outside of a car for a long time. In order to avoid inhaling harmful gases, this research implement an alarm system with a harmful gaseous substance sensor. By combining with windshield display technology, both driver and passengers are well informed about harmful gases concentration immediately. In addition, the system is integrated into smart device app and cloud system, which would provide further aids to the driver and passengers from remote. Since different windshields in different cars were required, this research accommodates various types of head-up display, develop air-substance sensor and interface set for smart devices so that implement a smart system for detecting toxic substances in the air of a car.